1. Technical Field
The present invention relates to the field of electrical engineering and is specifically concerned with electrical machines with a superconducting inductor and a gas cooling of normal-conductivity windings.
2. Background Art
There has been proposed an electrical machine (French Pat. No. 1,404,173) comprising a rotor and a stator, whereon windings are disposed. The stator winding is made of a superconducting alloy and arranged inside a cryostat intended to maintain temperatures at which the superconducting state of the winding is possible. The cryostat includes a set of coaxial cylinders interconnected at their end portions. The winding is cooled with a low-temperature liquid coolant which provides for the superconducting state of the winding, such as with liquid helium (He).
The rotor, mounted in rotation bearings and made of an epoxy resin reinforced with prestressed glass fibers, carries the rotor winding made of a normal-conductivity conductor, the rotor winding conductors having passages for a direct cooling.
The rotor is encompassed on the outside by the internal surface of the cryostat housing which is secured on the rotor rotation bearings. The cryostat with the superconducting stator winding is encompassed on the outside by a large-thickness ferromagnetic casing; the casing may be the outside wall of the cryostat housing and protect from the external atmospheric pressure.
The terms "external surface of the cryostat" and "internal surface of the cryostat" will hereinafter denote the cryostat housing surfaces which face the stator and the rotor respectively.
The use of a rotor winding with a direct cooling results in a non-uniform temperature distribution over the winding length, since the coolant is heated as it flows along the cooling passage provided inside the winding conductors. This heating causes a premature thermal ageing of the insulation in the zone of higher temperatures of the winding and hence impairs the operational dependability of the machines.
The fastening of the cryostat housing on the rotor rotation bearings causes the rotor vibration arising from a remaining unbalance of the rotor as well as the vibration originating in working members of driven mechanisms be transmitted to the stator's superconducting winding, which affects the stability of its operation and impairs the operational dependability of the machine.